Electric submersible motor oil expansion compensator

ABSTRACT

An electric submersible pumping system includes a motor that is filled with motor lubricant fluid and a pump driven by the motor. The electric submersible pumping system further includes a fluid expansion module connected to the motor that is designed to accommodate the expansion and contraction of the motor lubricant fluid in the motor. The fluid expansion module preferably includes a piston seal housing in fluid communication with the motor and a bag seal housing in fluid communication with the piston seal housing. The fluid expansion module further includes at least one axially movable barrier in the piston seal housing and at least one expansible barrier in the bag seal housing. The axially movable barrier and the expansible barrier cooperate to permit the expansion of the motor lubricant fluid without contaminating the motor lubricant fluid with fluids or and solids from the wellbore.

FIELD OF THE INVENTION

This invention relates generally to the field of submersible pumping systems, and more particularly, but not by way of limitation, to a system for accommodating the expansion of motor lubricants in high-temperature environments.

BACKGROUND

Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, the submersible pumping system includes a number of components, including one or more fluid filled electric motors coupled to one or more high performance pumps located above the motor. When energized, the motor provides torque to the pump, which pushes wellbore fluids to the surface through production tubing. Each of the components in a submersible pumping system must be engineered to withstand the inhospitable downhole environment.

Components commonly referred to as “seal sections” protect the electric motors and are typically positioned between the motor and the pump. In this position, the seal section provide several functions, including transmitting torque between the motor and pump, restricting the flow of wellbore fluids into the motor, protecting the motor from axial thrust imparted by the pump, and accommodating the expansion and contraction of motor lubricant as the motor moves through thermal cycles during operation. Prior art seal sections typically include a “clean side” in fluid communication with the electric motor and a “contaminated side” in fluid communication with the wellbore. Bellows or bags have been used to separate the clean side of the seal section from the contaminated side.

Recently, manufacturers have employed polymer expansion bags within the seal section to accommodate the expansion and contraction of motor lubricants while isolating the lubricants from contaminants in the wellbore fluid. Although generally effective at lower temperatures, the currently available polymers become somewhat permeable at extremely elevated temperatures and allow the passage of moisture across the membrane. The moisture reduces the insulating properties of polyimide and other films used to electrically isolate components within the downhole pumping system. Although piston-based systems may provide an alternative to the use of polymer expansion bags, prior art piston-based seal assemblies are susceptible to failure from sand, scale or other particulates. There is, therefore, a need for improved designs that can be used to accommodate expansion of motor fluids in elevated temperature applications. It is to this and other needs that the preferred embodiments are directed.

SUMMARY OF THE INVENTION

In preferred embodiments, the present invention includes an electric submersible pumping system that is configured to pump fluids from a wellbore. The electric submersible pumping system includes a motor that is filled with motor lubricant fluid and a pump driven by the motor. The electric submersible pumping system further includes a fluid expansion module connected to the motor that is designed to accommodate the expansion and contraction of the motor lubricant fluid in the motor.

The fluid expansion module preferably includes a piston seal housing in fluid communication with the motor and a bag seal housing in fluid communication with the piston seal housing. The fluid expansion module further includes at least one axially movable barrier in the piston seal housing and at least one expansible barrier in the bag seal housing. The axially movable barrier and the expansible barrier cooperate to permit the expansion of the motor lubricant fluid without contaminating the motor lubricant fluid with fluids or and solids from the wellbore.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a submersible pumping system constructed in accordance with a preferred embodiment of the present invention.

FIG. 2 provides a cross-sectional view of the motor, lower fluid expansion module and seal section constructed in accordance with a presently preferred embodiment.

FIG. 3 presents a cross-sectional representation of the motor of the pumping system from FIG. 2.

FIG. 4 presents a cross-sectional representation of the lower fluid expansion module of FIG. 2.

FIG. 5 presents a perspective view of a piston from the lower fluid expansion module of FIG. 4.

FIG. 6 presents a cross-sectional view of the sealing ring from the piston of FIG. 5.

FIG. 7 provides a cross-sectional view of the seal section of the pumping system from FIG. 2.

FIG. 8 provides a cross-sectional view of a mechanical seal from the seal section of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In accordance with a preferred embodiment of the present invention, FIG. 1 shows an elevational view of a pumping system 100 attached to production tubing 102. The pumping system 100 and production tubing 102 are disposed in a wellbore 104, which is drilled for the production of a fluid such as water or petroleum. As used herein, the term “petroleum” refers broadly to all mineral hydrocarbons, such as crude oil, gas and combinations of oil and gas.

The pumping system 100 preferably includes a pump 108, a motor 110, a seal section 112 and a fluid expansion module 114. The production tubing 102 connects the pumping system 100 to a wellhead 106 located on the surface. Although the pumping system 100 is primarily designed to pump petroleum products, it will be understood that the present invention can also be used to move other fluids. It will also be understood that, although each of the components of the pumping system are primarily disclosed in a submersible application, some or all of these components can also be used in surface pumping operations.

Generally, the motor 110 is configured to drive the pump 108. In a particularly preferred embodiment, the pump 108 is a turbomachine that uses one or more impellers and diffusers to convert mechanical energy into pressure head. In alternate embodiments, the pump 108 is configured as a positive displacement pump. The pump 108 includes a pump intake 118 that allows fluids from the wellbore 104 to be drawn into the pump 108. The pump 108 forces the wellbore fluids to the surface through the production tubing 102.

In the preferred embodiments, the seal section 112 is positioned above the motor 110 and below the pump 108. The fluid expansion module 114 is positioned below the motor 110. Although only one of each component is shown, it will be understood that more can be connected when appropriate, that other arrangements of the components are desirable and that these additional configurations are encompassed within the scope of preferred embodiments. For example, in many applications, it is desirable to use tandem-motor combinations, gas separators, multiple seal sections, multiple pumps, sensor modules and other downhole components.

It will be noted that although the pumping system 100 is depicted in a vertical deployment in FIG. 1, the pumping system 100 can also be used in non-vertical applications, including in horizontal and deviated wellbores 104. Accordingly, references to “upper” and “lower” within this disclosure are merely used to describe the relative positions of components within the pumping system 100 and should not be construed as an indication that the pumping system 100 must be deployed in a vertical orientation.

Referring now also to FIGS. 2 and 3, shown therein is a cross-sectional view of the seal section 112, motor 110 and fluid expansion module 114. As depicted in the close-up view of the motor 110 in FIG. 3, the motor 110 preferably includes a motor housing 120, stator assembly 122, rotor assembly 124, rotor bearings 126 and a motor shaft 128. The stator assembly 122 includes a series of stator coils (not separately designated) that correspond to the various phases of electricity supplied to the motor 110. The rotor assembly 124 is keyed to the motor shaft 128 and configured for rotation in close proximity to the stationary stator assembly 122. The size and configuration of the stator assembly 122 and rotor assembly 124 can be adjusted to accommodate application-specific performance requirements of the motor 110.

Sequentially energizing the various series of coils within the stator assembly 122 causes the rotor assembly 124 and motor shaft 128 to rotate in accordance with well-known electromotive principles. The motor bearings 126 maintain the central position of the rotor assembly 124 within the stator assembly 122 and oppose radial and axial forces generated by the motor 110 on the motor shaft 128.

The motor 110 is filled with non-conductive lubricating oil during manufacture that reduces frictional wear on the rotating components within the motor 110. As the motor 110 cycles during use and as the motor 110 is exposed to the elevated temperatures in the wellbore 104, the lubricating oil expands and contracts. It is desirable to prevent the clean motor oil from becoming contaminated with fluids and solids in the wellbore. To permit the expansion and contraction of the lubricating oil under elevated wellbore temperatures, the seal section 112 and fluid expansion module 114 are connected to the motor 110 and placed in fluid communication with the motor oil.

Continuing with FIG. 2 and referring now also to FIG. 4, shown therein is a cross-sectional view of the fluid expansion module 114. The fluid expansion module 114 includes a piston seal housing 130, a bag seal housing 132, one or more piston assemblies 134, a bag seal assembly 136 and a fluid exchange assembly 138. In a particularly preferred embodiment, the fluid expansion module 114 includes a pair of piston assemblies 134 a, 134 b. The piston assemblies 134 a, 134 b are placed in the piston seal housing 130 and are configured for axial movement within the fluid expansion module 114. The inside surface of the piston seal housing 130 includes a polymer liner 140 that reduces friction and stiction. The polymer liner 140 is preferably manufactured from PTFE, PFA, PEEK and other high-temperature polymers. Alternatively, the inside surface of the piston seal housing 130 can be manufactured from polished chrome, stainless steel or other durable metal.

Turning to FIG. 5, shown therein is a perspective view of one of the piston assemblies 134. The piston assembly 134 preferably includes a piston 142 and a pair of spring-energized seals 144. The piston 142 is preferably manufactured from a highly-polished metal, including chrome, stainless steel and related alloys and has an outside diameter that is only slightly smaller than the inside diameter of the piston seal housing 130. Alternatively, the piston 142 can be manufactured from a high-temperature rated elastomer or polymer. Preferred polymers of the piston 142 include polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA) and polyethether ketone (PEEK).

FIG. 6 presents a cross-sectional view of the seal 144. The seal 144 includes an body 146 and an interior spring 148. The body 146 is preferably manufactured from a durable, high-temperature and wear-resistant elastomer or polymer, such as polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA), polyethether ketone (PEEK) and perfluoroelastomer. The interior spring 148 is configured to exert force against the body 146 in an outward radial direction. In this way, the spring 148 presses the body 146 against the inside surface of the piston seal housing 130. The interior spring 148 is preferably configured as a coiled ring or series of connected Belleville washers.

Turning back to FIG. 4, the bag seal housing 132 includes the bag seal assembly 136. The bag seal assembly 136 preferably includes a bag support 150, a bladder 152, inlet ports 154 and discharge valves 156. The bag support 152 is rigidly attached to the inside surface of the bag seal housing 132. The bladder 152 is secured to the bag support 150 with compression flanges 158. Alternatively, the bladder 152 can be secured to the bag support 152 with grips or hose clamps. The inlet ports 154 provide a path of fluid communication from the piston seal housing 130 into the inside of the bladder 152 and bag support 150. Importantly, the bag support 150 permits the passage of fluids between the piston seal housing 130 and bag seal housing 132 only through the inlet ports 154. Fluids external to the bladder 152 are not allowed to pass directly into the piston seal housing 130.

The discharge valves 156 are preferably one-way relief valves that are configured to open at a predetermined threshold pressure that exceeds the exterior wellbore pressure. In this way, if the fluid pressure inside the bladder 152 exceeds the set-point pressure, the discharge valves 156 open and relieve the pressure inside the bladder 152 by discharging a small volume of fluid into the wellbore 104. In a particularly preferred embodiment, the bladder 152 is manufactured from a high-temperature polymer or elastomer. Suitable polymers and elastomers include polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA) and polyethether ketone (PEEK).

The bag seal housing 132 also includes the fluid exchange assembly 138. The fluid exchange assembly 138 includes a solids screen 160 and a plurality of exchange ports 162. The exchange ports 162 allow fluids to pass from the wellbore 104 through the solids screen 160 into the bag seal housing 132 around the exterior of the bladder 152. The solids screen 160 reduces the presence of particulates in the bag seal housing 132. The solids screen 160 is preferably manufactured from a metal or polymer fabric mesh.

During manufacture, the fluid expansion module 114 is filled with clean motor lubricant. The piston assemblies 134 a, 134 b are then placed into the piston seal housing 130. As the fluid in the motor 110 expands during operation, the increased volume exerts pressure on the upper side of the piston assembly 134 a. In response, piston assembly 134 a moves downward toward piston assembly 134 b. When the volume between the piston assemblies 134 a, 134 b decreases, the increased pressure on piston assembly 134 b forces it downward toward the bag seal housing 132. As piston assembly 134 b moves downward it pushes clean motor lubricant through the inlet ports 154, through the bag support 152 and into the bladder 152. The bladder 152 expands to accommodate introduction of fluid from the piston seal housing 130. As the bladder 152 expands, fluid external to the bladder 152 is expelled through the exchange ports 162 and solids screen 160. If the pressure inside the bladder 152 exceeds the threshold pressure limit of the discharge valves 156, the discharge valves 156 open and vent a portion of fluid into the wellbore 104.

Conversely, during a cooling cycle, the fluid in the motor 110 contracts and the movement of the components within the fluid expansion module 114 reverses. As the pistons 134 a, 134 b are drawn upward, fluid is pulled out of the bladder 152. As the volume and pressure inside the bladder 152 decreases, fluid from the wellbore is pulled into the bag seal housing 132 through the solids screen 160 and exchange ports 162. The fluid expansion module 114 provides a robust mechanism for allowing expansion and contraction of lubricants from the motor 110 while maintaining an isolation barrier between the clean motor lubricants and the contaminated fluids from the wellbore 104. Notably, the use of piston assemblies 134 a, 134 b provide redundant barriers to the bladder 152 that are not susceptible to the increased permeability found in even high-temperature bladders. Accordingly, even if the bladder 152 is exposed to extremely high temperatures and permits the passage of some moisture from the wellbore 104 into the piston seal housing 130, the moisture is isolated from the motor 110 by the redundant piston assemblies 134 a, 134 b.

In certain applications, it may be desirable to place the pump 108 below the motor 110. In those applications, the fluid expansion module 114 will be positioned above the motor 110 and the seal section 112 will be placed between the motor 110 and the pump 108. In these alternative embodiments, the bag seal housing 132 will actually be positioned above the piston seal housing 130.

Turning to FIG. 7, shown therein is a cross-sectional view of the motor 110 and seal section 112. The seal section 112 is attached to the upper end of the motor 110 and provides a second system for accommodating the sealing of the rotating shaft 128 to the equipment and support the thrust load of the pump 108. The seal section 112 includes a seal section shaft 164, a thrust bearing assembly 166, one or more mechanical seals 168 and one or more relief valves 170. During manufacture, the seal section 112 is filled with clean motor lubricant oil.

The seal section shaft 164 is coupled to the motor shaft 128, or formed as a unitary shaft with the motor shaft 128, and transfers torque from the motor 110 to the pump 108. The thrust bearing assembly 166 includes a pair of stationary bearings 172 and a thrust runner 174 attached to the seal section shaft 164. The thrust runner 174 is captured between the stationary bearings 172, which limit the axial displacement of the runner 174 and the motor shaft 128 and seal section shaft 164.

In a particularly preferred embodiment, the seal section 112 includes a plurality of mechanical seals. Two mechanical seals 168 a, 168 b are depicted in FIG. 7. As best illustrated in the close-up view of the mechanical seal 168 in FIG. 8, the mechanical seals 168 each include bellows 176, a coiled spring 178, a runner 180 and a stationary ring 182. These components cooperate to prevent the migration of fluid along the seal section shaft 164. The stationary ring 182 has an internal diameter sized to permit the free rotation of the seal section shaft 164. In contrast, the bellows 176, springs 178 and runner 180 rotate with the seal section shaft 164. The rotating runner 180 is held in place against the stationary ring 182 by the spring-loaded bellows 176. The bellows 176 preferably includes a series of folds that allow its length to adjust to keep the runner 180 in contact with the stationary ring 182 if the seal section shaft 164 should experience axial displacement. The bellows 176 may be manufactured from thin corrugated metal or from elastomers and polymers, including AFLAS, perfluoroelastomer, polytetrafluoroethylene (PTFE), perfluoroalkoxy (PFA) and polyethether ketone (PEEK).

Continuing with FIG. 7, the relief valves 170 are preferably one-way check valves that are spring-biased in a closed position. When a threshold pressure is exerted against the relief valves 170 by the internal pressure within the seal section 112, the relief valves 170 temporarily open to release fluid from inside the seal section 112 into the pump 108 or wellbore 104 to relieve the excess internal pressure.

Thus, during thermal cycling of the motor 110, the motor lubricant may expand from the motor 110 into the seal section 112 and the fluid expansion module 114. The fluid expansion module 114 provides the primary system for accommodating the expansion of fluid from the motor 110 and the seal section 112 provides a secondary system for accommodating the expansion of motor oil from the motor 110. In the event that the fluid inside the seal section 112 exceeds a threshold pressure, the relief valves 170 temporarily open to prevent damage to the motor 110 or mechanical seals 168. The primary function of the seal section 112 is to prevent migration of fluids along the shafts between the motor 110 and pump 108.

It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and functions of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. It will be appreciated by those skilled in the art that the teachings of the present invention can be applied to other systems without departing from the scope and spirit of the present invention. 

What is claimed is:
 1. An electric submersible pumping system for use in pumping fluids from a wellbore, the electric submersible pumping system comprising: a motor; a pump driven by the motor; and a fluid expansion module connected to the motor, wherein the fluid expansion module comprises: a piston seal housing; and a first piston assembly contained within the piston seal housing, wherein the first piston assembly is configured for sliding engagement within the piston seal housing.
 2. The electric submersible pumping system of claim 1, wherein the fluid expansion module further comprises a second piston assembly contained within the piston seal housing, wherein the second piston assembly is configured for sliding engagement within the piston seal housing.
 3. The electric submersible pumping system of claim 2, wherein each of the first and second piston assemblies comprises: a piston; and at least one seal positioned around the outside of the piston.
 4. The electric submersible pumping system of claim 3, wherein each seal further comprises: a body; and an interior spring, wherein the interior spring is configured to exert an outward radial force against the body.
 5. The electric submersible pumping system of claim 4, wherein the piston seal housing includes a polymer liner.
 6. The electric submersible pumping system of claim 1, wherein the fluid expansion module further comprises: a bag seal housing; and a bag seal assembly within the bag seal housing.
 7. The electric submersible pumping system of claim 6, wherein the bag seal assembly further comprises: a bag support; and a bladder secured to the bag support.
 8. The electric submersible pumping system of claim 7, wherein the bag seal assembly further comprises one or more discharge ports and wherein each of the one or more discharge ports is configured as a one-way check valve that places the interior of the bladder in fluid communication with the wellbore when opened.
 9. The electric submersible pumping system of claim 1, wherein the fluid expansion module further comprises a fluid exchange assembly and wherein the fluid exchange assembly comprises: a solids screen; exchange ports; and wherein the fluid exchange assembly is configured to place the exterior of the bladder in fluid communication with the wellbore.
 10. The electric submersible pumping system of claim 1, further comprising a seal section between the motor and the pump, wherein the seal section comprises: a shaft; one or more mechanical seals; and one or more relief valves.
 11. The electric submersible pumping system of claim 10, wherein each of the one or more mechanical seals comprises: a runner connected to the seal section shaft; and a stationary ring in contact with the runner.
 12. A system for accommodating the expansion of motor lubricant in a motor within an electric submersible pump used for removing fluids from a wellbore, the system comprising: a seal section connected to the motor; and a fluid expansion module connected to the motor, wherein the fluid expansion module has a longitudinal axis and wherein the fluid expansion module comprises: at least one piston assembly, wherein the at least one piston assembly moves along the longitudinal axis of the fluid expansion module in response to an expansion of the motor lubricant; and a bag seal assembly, wherein the bag seal assembly includes a bladder that expands in response to movement of the at least one piston assembly.
 13. The system of claim 12, wherein the fluid expansion module further comprises a fluid exchange assembly that places the exterior of the bladder in fluid communication with the wellbore.
 14. The system of claim 12, wherein the seal section comprises: a seal section shaft; and one or more mechanical seals connected to the seal section shaft.
 15. The system of claim 15, wherein the seal section further comprises at least one relief valve that is configured to release motor lubricant to the wellbore.
 16. An electric submersible pumping system configured to pump fluids from a wellbore, the electric submersible pumping system comprising: a motor; wherein the motor is filled with motor lubricant fluid; a pump driven by the motor; and a fluid expansion module connected to the motor, wherein the fluid expansion module comprises: a piston seal housing in fluid communication with the motor; a bag seal housing in fluid communication with the piston seal housing; at least one axially movable barrier in the piston seal housing; and at least one expansible barrier in the bag seal housing.
 17. The electric submersible pumping system of claim 16, wherein the at least one axially movable barrier in the piston seal housing comprises a piston assembly.
 18. The electric submersible pumping system of claim 17, wherein the at least one expansible barrier in the bag seal housing comprises a bladder.
 19. The electric submersible pumping system of claim 18, wherein the bladder has an interior that is in fluid communication with the piston seal housing and an exterior that is in fluid communication with the wellbore. 